Usually, ozone gas is generated by supplying oxygen gas supplied from an oxygen cylinder or separated from the air to an ozone generator. However, even when ozone gas is generated by using oxygen gas supplied from an oxygen cylinder, the generated ozone gas exists in the oxygen gas with only a concentration of about 5 to 10 vol %. Moreover, ozone gas has a property that it is strong in self-decomposability, and hence it self-decomposes while passing through an ozone-gas supply passage, the concentration becomes much lower in a stage where it is supplied to an ozone-gas consumption facility, and besides the supply-concentration is unstable. In the field of semiconductor production, the use of the oxidation activity of ozone in formation of an oxidation film on a substrate or the like is increasing. In this case, it is desired to supply ozone gas of a stable middle concentration so as to stably produce an oxidation film of an appropriate thickness within a short period of time.
From this point of view, a technique is known in which ozone gas is concentrated and purified by supplying ozone-oxygen mixture gas from an ozone generator to an adsorbing column filled with an ozone adsorbent (Patent Literature 1). In this case, in the case of condensing ozone by adsorbing it, however, the adsorbent is cooled to enhance its adsorbing ability, and the ozone-oxygen mixture gas is acted on the adsorbent retained in this low-temperature state, thereby causing the ozone gas to be preferentially adsorbed by the adsorbent so as to raise the temperature, or controlling the pressure in the adsorbing column so that the ozone gas is desorbed from the adsorbent. Therefore, there is a problem in that cooling/heating cycles and pressurizing/depressurizing cycles are required to concentrate ozone, with the result that extra energy is necessary and the apparatus is enlarged. In addition, the temperature of the adsorbent exerts a large influence on the condensing property. Consequently, there are further problems in that a prolonged time is required to lower the temperature of the adsorbent to a pre-determined one after the desorbing step, and that its control is complicated.
Therefore, the present applicant has proposed a technique in which an ozone-oxygen mixture gas is acted on an adsorbent in a non-cooled state to cause the ozone gas to be selectively adsorbed by the adsorbent, and the adsorbing column is vacuumed when performing an operation of desorbing the ozone gas, thereby desorbing the ozone gas from the adsorbent (Patent Literature 2).    Patent Literature 1: Japanese Patent Application Laid-Open No. 2003-171104    Patent Literature 2: WO2008-062534